1. Field of the Invention.
In regenerative heat exchange apparatus, a mass of heat absorbent material commonly comprised of packed element plates that form a heat absorbent matrix is positioned in a hot gas passageway to absorb heat from hot gases passing therethrough. After the plates become heated by the hot gas they are moved into a passageway for cool air where the heated plates transfer their absorbed heat to the cool air flowing therethrough.
As the hot exhaust gases are directed through the heat exchange apparatus, fly ash and unburned products of combustion carried by the exhaust gases are deposited on the surface of the packed element plates, and such deposits continue to be deposited and build up until air and gas flow through the heat exchanger are greatly retarded, if not substantially stopped. Heat is then generated in the deposits and the adjoining element to form a "hot spot" that, if not detected, will rapidly increase until the adjoining metal of the heat exchanger will itself ignite and cause a catastrophic fire.
2. Description of the Prior Art.
Recent developments in the use of infra-red ray detection apparatus to detect "hot spots" in a heat absorbent matrix of an air preheater in the manner disclosed by U.S. Pat. No. 3,861,458 of 1975 and U.S. Pat. No. 3,730,259 of 1973 have been extremely successful in carrying out their stated objective of signaling a potential "hot spot" or incipient fire well in advance of the occurrence of an actual damaging fire.
A subsequent U.S. Pat. No. 4,022,270 of 1977 was granted to define a series of detector "heads" that were moved in unison on independent lever arms to a position where they might "view" the potential "hot spots" and provide a signal that could be monitored by an operator. The detector heads were adapted to simultaneously move on arcuately movable arms to scan the heat absorbent matrix and then move back to an air lock where they could readily be cleaned or repaired for subsequent operation.
Frequently, however, lever arms supporting the detector heads would be slightly deformed or even radically bent so that they would fail to completely seat on the air lock while others would make a satisfactory seat in the manner originally proposed. Thus fly ash and unburned combustion products would continuously collect in some of the air locks not properly sealed, while further opening of an air lock door would create a flow passageway through the air lock permitting pressurized fluid from inside the heat exchanger to flow to the atmosphere.